Method for reducing metal oxides



June 9, 1964 c. K. MADER ETAL METHOD FOR REDUCING METAL OXIDES FiledNov. 4, 1960 United States Patent 3,136,623 METHUD FOR REDUCING METALOXIDES Charles K. Mader, Cold Springs, NX., and Juan Celada,

Monterrey, Nuevo Leon, Mexico, assignors of onehalf to PullmanIncorporated, Chicago, Ill., a corporation of Delaware, and of one-halfto Hoialata y Lamina, SA., Monterrey, Nuevo lLeon, Mexico, a corporationof Mexico Filed Nov. 4, 1960, Ser. No. 67,220 Claims. (Cl. '7S- 34) Thisinvention relates to a method for reducing metal oxides to their metals.In one of its aspects, the invention relates to a method for the directreduction of metal oxides, such as iron ores, and other iron oxides,with a reducing gas to convert these materials to their metallic ironstate, particularly into the form of pellets or masses of sponge ironwhich may be ground to a powder or employed as a melting stock forfurther use.

Prior to the present invention, processes heretofore proposed for theproduction of reduced iron in the form of porous solids, referred to assponge iron, comprise the conducting of an operation by either admixingthe raw iron with coal or coke, or by passing a reducing gas in contactwith a bed of iron ore or in contact with a mixed bed of iron ore andsolid reducing agents. It has been found, however, that these processeshave economic utility only when employed in the reduction of iron orewhere relatively small quantities of the ore are desired to be reduced.Thus, the processes heretofore proposed have been found to beeconomically unattractive by reason of the fact that they either fail toprovide for a relatively high degree of conversion of the iron ore tothe metallic iron and at a relatively high rate, or because they involvethe use of expensive raw materials in carrying out the reductiontreatment.

It is, therefore, an object of the present invention to provide a novelmethod for reducing metal oxides to their metals.

Another object of the invention is to provide a novel method forreducing iron ores, and other iron oxides to give metallic iron.

Still another object of the invention is to provide a novel method forthe reduction of iron ores, and other iron oxides, to produce spongeiron.

A further object of the invention is to provide a novel method forreducing iron ores to the metallic iron in the form of sponge iron, in ahigh degree of conversion and at a high rate.

A still further object of the invention is to provide a novel method forthe continuous reduction of iron ores to produce sponge iron, employinga continuous supply of a reducing gas having a uniform composition, andwhich may be maintained at a substantially relatively high and constanttemperature.

Other objects and advantages inherent in the invention will becomeapparent to those skilled in the art from the following description andthe accompanying drawing.

In accordance with the present invention, there is provided an improvedprocess for the direct reduction of metal oxides, for example, iron ore,or iron oxide materials, by passing a reducing gas or a reducing gasmixture through beds of the material or ore in a series of controlledsteps or stages comprising a system of reactors, in the mannerhereinafter described, to produce the sponge metal, for example, spongeiron, as a product 3,136,623 Patented June 9, 1964 r'icc of the process.In this manner, the aforementioned objects of the invention areattained, in that the ore, for example, hematite (FezOa), can be reducedto the extent of obtaining conversion on an average of up to about 95percent thereof in the form of metallic iron. This represents theremoval of up to about 97 percent of the oxygen which was originallypresent in the ore as ferrous oxide.

In general, the reduction operation is carried out in a reactor system,preferably comprising a battery of four reactors (or operation stages),although it will be understood that it is within the scope of theprocess of the present invention to provide for additional operation'and heat accumulators are connected by pipes in a manner which permitsby-passing a reactor-heat accumulator pair for maintenance and otherpurposes. The gas flow between the reactors is controlled by valves,which are operated from a control area. As more fully hereinafterdescribed, in operation, one of the four reactors is in a primaryposition, one in a secondary position, one in a cooling position and oneis being unloaded and loaded at any given time. In operating at thedesign capacity, each reactor remains in each of the four positions (inone embodiment of the process of the present invention), for a periodsuch as three hours, thus resulting in a total cycle time of twelvehours for each reactor.

The primary gas employed for reducing the raw ore, is generally producedfrom atmospheric air and reducing gases which contain carbon monoxideand hydrogen as principal components. Reducing gases that are high incarbon monoxide and hydrogen can be produced, for example, from naturalgas and then mixed with steam and then catalytically converted to carbonmonoxide and hydrogen in accordance with known commercial operations. Itis also possible, in this respect, to employ a conventional Water-gasreaction to produce the desired reducing gas. In a preferred embodimentof the present invention, the reducinggas employed for carrying out thereduction operations, may be obtained by desulfurization of natural gas,which is split into several streams. Each stream is then mixed withsuperheated steam and passed through a convection section of one of aseries of reformer furnaces, normally employed in reforming operations.From the individual convection sections, the preheated gas stream passesinto the radiant section of the reformer furnace where the natural gasreacts, in vertical tubes which are packed with catalytic materiaLwiththe steam to form carbon monoxide and hydrogen. The gas stream is thenpassed through the waste heat boiler to recover the sensible heat fromthe gas. In order to minimize cooling-water requirements, each gasstream is passed through an air cooler before all of the individualstreams are combined and cooled in a reformer quench tower. Thesequenched products, referred to as primary gas, comprise about percentcarbon monoxide and hydrogen.

The cold primary gas from the aforementioned reformer quench tower, isintroduced into a reactor which is in the cooling position of thereduction cycle. In this reactor, the primary gas is heated by hotsponge iron. During cooling of the product, carbon is deposited in thebed by the reducing gas which may be enriched by the addition of naturalgas.

This has been found to aid quality control of the product during thesubsequent melt. From the cooling reactor, the gases pass through Y thecooling reactor heat accumulator, the primary re- The bulk of the oxygenremoval is carprises the finishing step, results in the removal of stillmoreV oxygen, representing a product from which up to about 80 to 90percent of the oxygen present in the original raw ore product has beenremoved.

Each of the reactors is provided with a combustion chamber, notillustrated, for the sake of simplicity. During the primary andsecondary steps, air is injected in the gas stream to raise thetemperature level of the gas to temperatures in the range ofapproximately 1300" F. to 2500" F. ln most operations, temperaturesbetween about 1800" F. and about 2200" F. are preferred. In order toavoid possible sticking or agglomeration of the metal particles, it ispreferred that the average temperature maintained in the secondary step,be approximately 100" F. lower than that maintained in the primary step.The air employed in the partial oxidation is compressed and preheatedlto temperatures within the range of about 1200" F. to about 1800" F. ina tubular air preheat furnace. Temperatures between about 1400" F. toabout 1600" F. are generally preferred for the optimum utility from aneconomic standpoint. VThe gas stream from the secondary heat accumulatoris cooled to a temperature between about 120 F. and about 200 F. by theinjection of water into the effluent line. Preferably, the gas stream iscooled to a temperature between about 150" F. and about 175 F. Furthercooling of the gas stream to a temperature below about 100 F., dependingupon the temperature of the cooling water introduced, is effected in thefuel quench tower, where water vapor resulting from the oxidation of theprocess gas is condensed. The resulting tail gas comprising as a majorcombustible component, carbon monoxide and hydrogen, is employed as afuel gas. Natural gas may be added to the fuel gas, as required tosatisfy the fuel requirements of the plant. The cold sponge iron is thenremoved through the bottom of the reactor, and is then ready for furtheruse.

To maintain the necessary reduction conditions in the r-espectivesecondary, primary and cooling zones, the composition and temperature ofthe respective components comprising the gaseous reducing mixture,constitute a critical feature of the present process. In this respect,it will be noted that the reducing gas itself, may comprise hydrogen,carbon monoxide or mixtures thereof. Oxygen employed for combustion toraise the temperature of the reducing gas to that required for carryingout the reduction of the iron ore, as discussed above,

may comprise either pure oxygen or an oxygen-containingV gas, such asair. In order to carry out the desired degree of reduction in each ofthe aforementioned three reactors, it has been found that the ratio ofoxygen to the reducing gas should be lower in thesecondary reactor thanthat employed in the primary reactor.

To achieve the desired reducing temperatures in each stage, the oxygenor oxygen-containing gas is introduced into the respective combustionchambers of the primary and secondary reactors at temperatures betweenabout 60" Ff and about 1800" F. When pure oxygenris employed, it ispreferred .that it be introduced into the combustion section ofthereactor at a temperature between about 60" F. and about 100" F. Wherethe oxygen is present in the form of air, the latter is preferablyintroduced into the combustion section of the reactors at temperaturesbetween about l400 F. and about 1600" F.

The reducing gas, for example, hydrogen, carbon monoxide or mixturesthereof, or gases containing these components, is introduced intothecombustion chambers of the primary and secondary reactors attemperatures between about 60" F. and about 1800" F. lt is preferred,however, to introduce the reducing gas into the primary reactor at atemperature between about 600 F. and about 1600" F. In the secondaryreactor, the reducing gas is preferably introduced at a temperaturebetween about 1500" F. and about 1600" F. The reducing gas employed inthe cooling reactor is preferably introduced at a temperature between 60F. and about 100" F.

In a normal operation, a different reactor is recharged with the ore andstarted, at predetermined intervals (for example, every three hours)progressing in numerical order through the battery of the reactors (forexample, a battery of four reactors, namely, from the first through thefourth reactor and then back, once more, to the first reactor). Thus,the charge, in a battery of four reactors, will pass through threereduction stages of three hours each, in each reactor. These threereduction stages comprise (l) a hot reduction treatment with partiallyspent hydrogen-rich gas; (2) a hot reduction treatment with gas ofnearly full strength; and (3) a completion of the reduction treatmentwhile cooling down with fullstrength cold gas. After the ore is passedthrough the aforementioned three reduction stages, there follows areactor shut-down period for the removal of the sponge iron from a givenreactor, which is then refilled with fresh ore. The operating cycle, itwill be noted, also provides an additional three hours to put thereactor through the aforementioned fourth period.

As will be noted from the above, four operating stages have beenprovided for completing the ore reduction cycle. These four operatingstages are referred to and described as follows: (a) secondary operatingstage-in which the treating gas is in its second' hot reducing stage,although the ore is in Vits first stage of reduction; (b) primaryoperating stage-in which the gas is in its first hot reducing stage,although the ore is in its second stage of reduction; (c) coolingoperating stage-in which the ore is undergoing cooling and is in itslast stage of reduction, while the gas is being heated; and (d)turnaround operating or production stage-in which the reduced ore (eg,sponge iron) is removed from the reactor, completing the cycle, and thereactorl is recharged for the commencement of a new cycle. Every threehours, a recharged reactor (i.e., the reactor which has just completedits turnaround) is started inicycle, and each of the other threereactors is placed in the next stage of its cycle by changing the pointsof gas entry and exit in the reactor battery. This shifting of the gasflow, progressively through the battery with the numerically firstreactor following the fourth reactor,l provides a countercurrent flow ofgas against thefadvancing stages of the ore treatment.

It will be seen from the foregoing description that the reactor batterypasses through the following four alignments duringa typical 12-hourcycle (assuming that the first reactor ie., numerical reactor l, startscooling at 0 hours):

Reactor 0-3 hours 3-6 hours y 6-9 hours 9-12 hours Co olng TurnaroundSeconary Primary. Primary. Cooling Turnaround. Secondary. SecondaryPrimary Cooling Turnaround. Turnaround Secondary Primary Cooling.

When a particular reactors cooling stage is completed, the vessel andits attendant equipment are purged. The sponge iron is then unloadedafter removing the heads and inner door, upon which the load rests inthe bottom of the reactor.

In order to provide a better understanding of the irnproved process ofthe present invention, reference is had to the accompanying drawingwhich forms a part of this specification and illustrates,diagrammatically, an elevational view of one form of the apparatusemployed and capable of carrying out a preferred embodiment of theinvention. It should be understood, however, that it is not intendedthat the invention be limited to the ernbodi` ment or example asillustrated, but is capable of other embodiments which may extend beyondthe scope of the apparatus illustrated. Some of thernechanical elementsnecessary to effect the transfer of solids, liquids and vapors tomaintain the necessary operating conditions to carry out the functionsof the apparatus, have been omitted in order to simplify thedescription. Furthrmore, in the discussion of the drawing, it will benoted that the handling of the gas ow and the treatment and conveyanceof the metal oxides or ores, are separately described for the purpose ofsimplification.

Referring to the drawing, natural gas is introduced into the systemthrough conduit at the rate of 13,900 s.c.f./ton of iron in the ore.This gas may comprise natural gas previously subjected to a conventiondesulfurization treatment, if so required. The gas from conduit 10 isnext transferred to a reformer furnace 14, which is a conventionalhydrogen-producer or catalytic gas/ steam reactor. This feed gasentering the reformer furnace 14 through conduit 10 is merged withsuperheated steam coming from steam drum 16 via conduit 18 and thefurnace stack superheater coil at the rate of 1530 pounds per ton of theiron in the ore. Excess steam produced in the superheater coil isremoved via conduit 20 for further use where so desired. The mixture offeed gas and super* heated steam heated, in a conventional manner, inthe tubes (not shown) of the preheater section in the bottom of thefurnace stack, flows downwardly to the radiant portion of the furnacevia conduit 24, and is distributed through vertical tubes (not shown)which are filled with catalytic material, for example, a nickel catalystsupported on an alumina base. It the reformer furnace 14, the naturalgas/steam feed is heated to a temperature of about 1500 F.

Water employed for producing steam in drum 16 is introduced via conduit26. Unvaporized water from drum 16 is transferred into the stack offurnace 14 via line 28.V After being converted to steam in furnace 14,the latter is returned to drum 16 via line 30.

From reformer furnace 14, the hydrogen-rich effluent or process gas,comprising hydrogen and carbon monoxide, is subjected to a coolingtreatment by being transferred through conduit 32 to a waste-heat boiler34. Waste-heat boiler 34 may, if so desired, also be replaced by a heatexchanger. Boiler 34, in the system illustrated, operates on aconvective water circuit from steam drum 16. For this purpose, water istransferred from steam drum 16, via conduit 36, to boiler 34. Eflluentsteam from boiler 34 is withdrawn and transferred through conduit 38 tosteam drum 16, for use. From boiler 34, the cooled process gas istransferred via conduit 40 to a reformer quench or spray tower 42, whereopen water, introduced through conduit 44, cools the gas stream t0 atemperature within the range from about 60 F. to about 100 F., as thegas flows up through Raschig rings positioned within the tower. Excesssteam, i.e., steam not consumed in reformer furnace 14, is condensed intower 42 and removed, together with cooling water, from the system viaconduit 46.

The cooled process gas from tower 42 is withdrawn through conduit 48 andcomprises from about 70 to 75 percent hydrogen. The remaining componentsin this gas comprises methane, carbon monoxide, carbon dioxide and watervapor. Natural gas may also be added to the process gas in yconduit 48,via conduit 50, so that the methane content of the process gas may beincreased, if so desired. Tower 42 is held at a pressure of about 55p.s.i.g. to provide sufficient pressure for the transfer of the 6.cooled process gas, via conduit 43, to each reactor as it assumes theposition of the cooling stage as shown by cooling reactor 52. At thispoint, it should be noted that for the purposes of this description, itwill be assumed that reactor 52 is in the cooling stage, reactor 54 isin the primary reduction stage, reactor 56 is in the secondary reductionstage, and reactor 58 is in the turn around or production stage, by theproper manipulation of suitable valve arrangements, which have beenomitted from the drawing for the sake of simplicity.

Continuing with the ow of cooled gas from tower 42, and augmented bynatural gas which is introduced through conduit 50 if desired, the gasstream is transferred via conduit 48 at the rate of 50,000 s;c.f./ton ofiron in the ore to reactor 52, which is in the cooling position, to thecombustion section or chamber (not operating in the cooling stage), tothe space above the ore bed of reactor 52 and through the hot bed (whichis now cooling after having been in the primary stage of reactor 54).From reactor 52, the reducing gas, as it passes through conduit 60 andthrough heat accumulator 62, is heated to a temperature between about600`F. and about l600 F. From accumulator 62, the gas is withdrawnthrough conduit 64 to the combustion section of primary reactor 54. Inreactor 54, preheated air is injected from air-preheater 66, viaconduits 68, 70 and 64, in an air to gas ratio of about 0.15 to 0.25, tobring the stream up to a temperature of about 1900 F. to 2200" F. Fromreactor 54, the hot gas is withdrawn and transferred through conduit 7 2to a heat accumulator 74, where it is maintained at a temperature ofabout 1500 F. to 1600 F. This gas, together with additional preheatedair, in an air to gas ratio of about 0.15 to 0.25, from conduit 70 tobring the stream up to proper bed entry temperatures of about l800 F. to2000 F., is next transferred via conduit '76 to secondary reactor 56.After passing through thefresh ore of reactor 56, the gas is, from apractical standpoint, considered as spent. From reactor 56, the spentgas is Withdrawn and transferred through conduit 78 to heat accumulator80. This gas is withdrawn through conduit S2 at a temperature betweenabout 200 F. and about 1600 F.

It will be noted, at this point, that the gas in conduit 82 isrblockedoff from production reactor 58, which is in the unloading/loading orturnaround stage. The spent gas from accumulator is transferred viaconduits 82 and 84 (in admixture with further quantities of coolingwater introduced into conduit 84) into a packed spray or fuel quenchtower S6. Additional quantities of cooling water are introduced intotower 86 via conduit 88. The cooling water employed in tower 86 iswithdrawn via conduit 90 and, in combination with cooling water fromtower 42, is transferred via conduit 46 to a degassing or gaselimination treatment, not shown. The cooled spent gas from tower 86 iswithdrawn via conduit 12 for further use in furnace 14 as fuel gas. Thismay be augmented by the addition of natural gas introduced via conduit22. A portion of this gas may be withdrawn from conduit 12 via conduit92. This gas may be transferred into air preheater 66 for use as a fuelgas, for heating air which is introduced into preheater 66 throughconduit 94. Water, employed for use in steam drum 16, is introducedthrough conduit 96 into preheater 66. It will be noted, in the drawing,that reactor 58 is illustrated in the turnaround position. This reactoris also employed in conjunction with its own heat accumulator 98 whichis joined to reactor 58 by conduit 100. Gases from accumulator 98 arewithdrawn Via conduit 102 for use in the process, as previouslydescribed. The fresh ore charge employed in the process is introducedinto reactor 58 through conduit 104, and the nal reduced sponge ore'product is removed from reactor 58 through outlet means 106. It willalso be noted, as shown in the drawing, that reactor 58, following thedischarge of reduced ore is now also ready to assume the secondaryreaction stage, in the position occupied -by reactor 56, as shown.

Considering now the treatment and conveyance of the metal oxide or orebeing treated, which, for the purposes of this example, comprising rawhematite (Fe203) ore, a predetermined mass of the ore, is introducedthrough conduit 104 into production reactor 58 (which is in theunloading or turnaround position, as illustrated in the drawing). Byproper valve manipulation (not shown), reactor 58 is brought into thesecondary reactor position as illustrated by reactor 56. As previouslyindicated, preheated air at a temperature between y.about 1400c F. `and1600 F. in conduit d is injected into the gas stream in conduit '76, viaconduit 70, to raise the temperature level of the gas to approximatelyl800 F. to 2000 F. and at this temperature is introduced into reactor56. Secondary reactor 56 serves as a preheating and partial reductionstage. After being maintained in this position for a period of threehours (employing a typical lZ-hour cycle for a complete production),approximately 38 percent of the oxygen present in the ore as metallicoxide has been removed. Following the partial reduction stage asillustrated by reactor 56, reactor 58 is next brought into the primaryreactor position, illustrated by reactor 54;. In reactor 54, preheatedair from conduit 70 is injected into the gas stream in conduit 64 toraise the temperature level of the gas to a temperature of 1900 F. to2200 F. and at this temperature is introduced into reactor 54. Primaryreactor 54 serves as a means for carrying out the bulk of the oxygenremoval. In reactor 54, an additional 42 percent of the oxygen presentin the ore is removed during a period of three hours, representing atotal oxygen removal of approximately 80 percent. Following thereduction treatment as illustrated by reactor 54, by proper valvemanipulation, reactor 58 is brought into the cooling reactor position,illustrated by reactor 52. In reactor 52, process gas in conduit 48,augmented by natural gas introduced through Y conduit 50, if so desired,is introduced at a temperature of 60 F. to 100 F. into the reactor. Fora period of three hours, the final reduction treatment therein resultsin obtaining a reduced ore product from which approximately 90 percentof the oxygen originally present in the raw ore product has beenremoved. Following the treatment in reactor 52, this reactor is thenbrought into the position of production reactor 58, by proper valvemanipulation Where, after undergoing a sponge iron removal period, isthen ready for a fresh charge and a repetitive treatment Vof the newlyadded ore. As previously indicated, every three hours a rechargedreactor (i.e., the reactor which has just completed its turnaround orproduction stage) is started in the cycle with each of the other threereactors being placed in the next stage of its cycle,

by changing the points of the process gas entry and exitV inthe reactorbattery. It will thus be seen that the aforementioned shifting of thegas ow progressively through the battery of reactors, with thenumerically rst reactor following the fourth reactor, .results inbringing a countercurrent fiow of gas against each advancing stage ofthe ore treatment.

In carrying out the aforementioned operation, certain manipulativeoperations are preferably observed and employed. In this respect, it isfound that the rate of oxygen removal from the ore increases with highertemperature, and therefore it is found that variations in the pn'- maryand secondary stage combustion air ratios may be employed to affect therate of reduction. If temperatures above 1800 F. are employed, care mustbe exercised to avoid fusing .the reactor load. The temperature lattheinlets to the heat accumulators are employed as a check of thetemperature conditions maintained in their corresponding reactors.

The rate of reduction activity has been found to depend upon the amountand temperature of reducing gases that are `available during thereaction with the ore. In

,eze

general, the improved process of the present invention requires Aarelatively large quantity of hydrogen in excess of the amount which isactually consumed in the treatment within each reactor. In this respect,it is found that the ore reduction usually consumes about one-half ofthe hydrogen which is produced in the reformer furnace. Of thisquantity, a small amount is yconsumed in the combustion chambers, withthe remainder being withdrawn for use -as a fuel gas.

The following equations serve to illustrate the specific reductionswhich koccur within the reactors. In these equations, hydrogen isshown-as the reducing agent, although carbon monoxide will remove someof the oxygen content of the ore, particularly at lower temperatures,employed in the cooling stage. Excess hydrogen tends to drive thesereactions towards completion.

(1) 3Fe2O3-l-H2:2Fe304(magnetic ore) -l-HZO (2) Fe3O4+H2=3FeO (ferrousoxide) -i-HZO (s) Feo+H2=Fe+H2o Reaction 3 does not occur yas readily asReactions 1 Vand 2, and is aided by high hydrogen and low watervaporconcentrations. Therefore, the conditions in the primary reactor stageand the beginning of the cooling stage will encourage completion of theore reduction.

The extent of the reduction of the ore, it should be noted, is alsodependent upon 'the time of exposure to the process gas, unless thecycle in use is bringing the gas and ore nearly to equilibrium in thehot and cold stages. As will be seen from the foregoing discussion, thereaction time is 9 hours (viz., from the beginning of the ore heating tothe end of the cooling operation) in a 12-hour cycle being used in theembodiment shown. However, it should be noted that the ore is alsoundergoing satisfactory reduction conditions for a shorter period. Ifthe remaining conditions are unchanged, it is found that the shorteningof the reduction time will have a tendency to leave a higher oxygencontent in the sponge iron. Thus, it is within the scope of the presentinvention to operate for shorter reduction cycles, or with changes inlength of stages within the l2-hour cycle. The time factor can beemployed to offset some loss in gas eiciency when one reactor is shutdown for repair or maintenance purposes. The three remaining reactorscan then be placed on -a longer cycle, even though such action mayresult in decreased capacity. When only 'three reactors are operable,the turnaround stage can be shortened as much as possible so as toobtain some secondary stage reaction on each fresh load of ore, beforeplacing it in the primary stage.

As previously indicated, the reformer furnace or series of reformers areemployed to catalytically react hydrocarbons principally with steam toproduce hydrogen and oxides of carbon. An excess of steam is employed inorder tol cause the reaction to progress. lf a sucient excess of steamis employed, it is found that carbon formation and its deposit upon thecatalyst is prevented. Generally, steam to gas ratios may be employed ashigh as 3.0 to 1.0 (on a mol basis) to remove carbon. Ratios of about2.2 to 1.0 are preferred. In general, it has been found expedient tokeep this ratio high whenever reformer operation or rate of feed gasdelivery is irregular. Lower steam ratios tend to produce some carbonmonoxide in the reformer eiuent, and increased amounts of carbon ormetal components as copper, phosphorus or nickel, which are handled inaccordance with the treatment described, to produce the correspondingelemental metal or metallic spongy masses. In addition, it should benoted that while a particular embodiment of the improved process of thepresent invention has been described for purposes of illustration,various modifications and adaptations thereof, which will be obvious tothose skilled in the art may be made Within the spirit of the inventionand without departing from its scope.

We claim:

l. A method for reducing metal oxides which comprises: in a rstreduction treatment, mixing a stream comprising an oxygen-containing gasmaintained at a temperature between about 60 F. and about 1800 F. and astream comprising a partially spent reducing gas, said partially spentreducing gas being an eiuent of and conveyed from a second reductiontreatment conducted simultaneously with said first reduction treatmentand maintained at an elevated temperature for combustion with oxygen insaid oxygen-containing gas, in a mol ratio such that the mixture isheated to a reducing temperature, contacting a mass of metal oxide withthe resulting gaseous mixture to reduce a portion of said metal oxide;in a second reduction treatment, mixing a stream comprising anoxygen-containing stream maintained at a ternperature of about 60 F. andabout 1800D F. and a stream comprising a reducing gas said reducing gasbeing an effluent of and conveyed from a third reduction treatmentconducted simultaneously with said second reduction treatment andmaintained at an elevated temperature for combustion With oxygen in saidoxygen-containing gas, the mol ratio of oxygen to reducing gas beinggreater than that employed in said first reduction treatment such thatthe resultant gaseous mixture is heated to an elevated reducingtemperature, contacting a mass of said partially reduced metal oxidefrom said rst reduction treatment with the resulting gaseous mixture tofurther reduce a portion of said metal oxide to 'the metallic state; andin a third reduction treatment contacting a mass of said partiallyreduced metal oxide from said second reduction treatment with a streamcomprising a reducing gas to reduce a further portion of said partiallyreduced metal oxide to the metallic state. l

2. A method for reducing metal oxides which comprises: in a rstreduction treatment, mixing a heated stream comprising at least oneOxygen-containing gas selected from the group consisting of oxygen andair maintained at a temperature between' about 60 F. and

about 1800 F. and a stream comprising a partially spent a reducing gas,said partially spent reducing gas being an eiuent of and conveyed from asecond reduction treatment conducted simultaneously with said rstreduction treatment and maintained at an elevated temperatureforcombustion with oxygen in said oxygen-containing gas, in a mol ratiosuch that the mixture is heated to a reducing "temperature, contacting amass of metal oxide with the resulting gaseous mixture to reduce aportion of said metal oxide; in a second reduction treatment, mixing astream comprising an oxygen-containing stream maintained at atemperature of about 60 F. and about 1800 F. and a stream comprising areducing gas, said reducing gas being an eiiuent of and conveyed from athird reduction treatment conducted simultaneously with said secondreduction treatment and maintained at an elevated temperature forcombustion with oxygen in said oxygen-containing gas, the mol ratio ofoxygen 'to reducing gas being greater than that employed in said firstreduction treatment such that the resultant gaseous mixture is heated toan elevated reducing temperature; contacting a mass of said partiallyreduced metal oxide from said first reduction treatment with theresulting gaseous mixture to further reduce a portion of said metaloxide to the metallic state; and in a third reduction treatmentcontacting a mass of said partially reduced metal oxide from said secondreduction treatment with a stream comprising at least one reducing gasselected from the group consisting of hydrogen and carbon monoxide toreduce a further portion of said partially reduced metal oxide to themetallic state.

3. A method for reducing metal oxides which comprises: in a rstreduction treatment, mixing a stream comprising an oxygen-containing gasmaintained at a temperature between about 60 F. and about 1800 F. and astream comprising a partially spent reducing gas, said partially spentreducing gas being an eiuent of and conveyed from a second reductiontreatment conducted simultaneously with said first reduction treatmentand maintained at an elevated temperature for combustion with oxygen insaid oxygen-containing gas, in a mol ratio such that the mixture isheated to a reducing temperature, contacting a mass of metal oxide withthe resulting gaseous mixture to reduce a portion of said metal oxide;in a second reduction treatment, mixing a stream comprising anoxygen-containing stream maintained at a temperature of about 60 F. andabout 1800 F. and a Stream comprising a reducing gas, said reducing gasbeing an efliuent of and conveyed from a third reduction treatmentconducted simultaneously With said second reduction treatment andmaintained at an elevated 'temperature for combustion with oxygen insaid oxygen-containing gas, the mol ratio of oxygen to reducing gasbeing greater than that employed in said rst reduction treatment suchthat the resultant gaseous mixture is heated to an elevated reducingtemperature, contacting a mass of said partially reduced metal oxidefrom said iirst reduction treatment with the resulting gaseous mixtureto further reduce a portion of said metal oxide to the metallic state;and in a third reduction treatment contacting a mass of said partiallyreduced metal oxide from said second reduction treatment with a streamcomprising a reducing gas maintained at a temperature between about 60F. and about F. to reduce a further portion of said partially reducedmetal oxide to the metallic state.

4. A method for reducing iron ore to produce sponge iron whichcomprises: in a rst reduction treatment, mixing a stream comprising anoxygen-containing gas ,maintained at a temperature between about 60 F.and about 1800 LF. and a stream comprising a partially spent reducinggas, said partially spent reducing gas being an efuent of and conveyedfrom a second reduction treatment conducted simultaneously with saidfirst reduction treatment and maintained at an elevated temperature forcombustion with oxygen in said oxygen-containing gas, in a mol ratiosuch that the mixture is heated to a reducing temperature, contacting amass of iron ore With the resulting gaseous mixture to reduce a portionof said ore; in a second reduction treatment, mixing a stream comprisingan oxygen-containing stream maintained at a temperature of about 60 F.and about 1800" F. and a stream comprising a reducing gas said reducinggas being an eiiiuent of and conveyed from a third reduction treatmentconducted simultaneously with said second reduction treatment andmaintained at an elevated temperature for combustion with oxygen in saidoxygen-conaining gas, the mol ratio of oxygen to reducing gas beinggreater than that employed in said first reduction treatment such thatthe resultant gaseous mixture is heated to an elevated reducingtemperature, contacting a mass of said partially reduced iron ore fromsaid first reduction treatment with the resulting gaseous mixture tofurther reduce a portion of said ore to sponge iron; and in a thirdreduction treatment contacting a mass of said partially reduced iron orefrom said second reduction treatment with a stream comprising a reducinggas to reduce a further portion of said partially reduced ore to spongeiron.

5. A cyclic process for reducing iron ore to produce sponge iron whichcomprises: in a iirst reduction treatmen't, mixing a stream comprisingan oxygen-containing gas maintained at a temperature between about 60 F.and about 1800 F. and a stream comprising a partially aiseeaa spentreducing gas, said partially spent reducing gas being an effluent of andconveyed from a second reduction treatment conducted simultaneously withsaid lirst reduction treatment and maintained at an elevated temperaturefor combustion with oxygen in said oxygen-containing gas by supplyingthereto heat accumulated in the prior cycle, in a mol ratio such thatthe mixture is heated to a reducing temperature, contacting a mass ofiron ore with the resulting gaseous mixture to reduce a portion of saidore; in a second reduction treatment, mixing a stream comprising anoxygen-containing stream maintained at a temperature of about 60 F. andabout 1800 F. and a stream comprising a reducing gas said reducing gasbeing an eiuent of and conveyed from a third reduction treatmentconducted simultaneously with said second reduction treatment andmaintained at an elevated temperature for combustion with oxygen in saidoxygencontaining gas, the mol ratio of oxygen to reducing gas beinggreater than that employed in said iirst reduction treatment such thatthe resultant gaseous mixture is heated to an elevated reducingtemperature, contacting a mass of said partially reduced iron ore fromsaid iirst reduction treatment with the resulting gaseous mixture tofurther reduce a portion of said ore to sponge iron; and in a thirdreduction treatment contacting a mass of said partially reduced iron orefrom said second reduction treatment with a stream comprising a reducinggas maintained at a temperature between about 60V F. and about 100 F. toreduce a further portion of Said partially reduced ore to sponge iron.

6. A method for reducing iron ore to produce sponge iron whichcomprises: in a first reduction treatment, mixing a stream comprising anoxygen-containing gas maintained at a temperature between about 60 F.and about l800 F. and a stream comprising a partially spent reducing gassaid partially spend reducing gas being an eiiluent of and conveyed froma second reduction treatment conducted simultaneously with said iirstreduction treatment and maintained at an elevated temperature betweenabout 60 F. and about 1600 F., in a mol ratio such that the mixture isheated to a reducing temperature, contacting a mass of iron ore with theresulting gaseous mixture to reduce a portion of said ore; in a secondreduction treatment, mixing a stream comprising an oxygencontainingstream maintained at a temperature of about 60 F. and about 1800 F. anda stream comprising a reducing gas said reducing gas being an effluentof and conveyed from a third reduction treatment conductedsimultaneously with said second reduction treatment and maintained at anelevated temperature between about 1500 F. and about 1600 F., the molratio of oxygen to reducing gas being greater than that employed in theiirst reduction treatment such that the resultant gaseous mixture isheated to an elevated reducing temperature, contac'ting a mass of saidpartially reduced iron ore from said first reduction treatment with theresulting gaseous mixture to further reduce a portion of said ore tosponge iron; and in a third reduction treatment contacting a mass ofsaid partially reduced iron ore from said second reduction treatmentwith a stream comprising a reducing gas maintained at a temperaturebetween about 60 F. and about 100 F."to reduce a further portion of saidpartially reduced iron ore to sponge iron;

7. A method for reducing iron ore to produce sponge iron whichcomprises: in a irst reduction treatment, mixing a stream comprisingoxygen maintained at a temperature between about 60 F. and about 100 F.and a stream comprising a partially spent reducing gas, said partiallyspent reducing gas being an eiliuent of and conveyed from a secondreduction treatment conducted simultaneously with said iirst reductiontreatment and maintained at an elevated temperature for combustion withoxygen, in a mol ratio such that the mixture is heated to a reducingtemperature, contacting a mass ot iron ore with the resulting gaseousmixture to reduce Aa portion of said ore; in a second reductiontreatment, mixing a stream comprising oxygen maintained at a temperatureof between about 60 F. and about 100 F., and a stream comprising areducing gas said reducing gas being an eiiiuent of and conveyed from athird reduction treatment conducted simultaneously with said secondreduction treatment and maintained at a suitably elevated temperaturefor combustion with oxygen, the mol ratio of oxygen to reducing gasbeing greater than that employed in said rst reduction treatment suchthat the resultant gaseous ixture is heated to an elevated reducingtemperature, contacting a mass of said partially reduced iron ore fromsaid irst reduction treatment with the resulting gaseous mixture tofurther reduce a portion of said ore to sponge iron; and in a thirdreduction treatment contacting a mass of said partially reduced iron orefrom said second reduction treatment with a stream comprisinga reducinggas maintained at a temperature between about 60 F. and about F. toreduce a further portion of said partially reduced ore to sponge iron.

8. A method for reducing iron ore to produce sponge iron whichcomprises: in a first reduction treatment, mixing a stream comprisingair maintained at a temperature between about 1400 F. and about 1600 F.and a stream comprising a. partially spent reducing gas, said partiallyspent reducing gas being an eiuent of and conveyed from a secondreduction treatment conducted simultaneously with said first reductiontreatment and maintained at an elevated temperature for combustion withoxygen in ,said air, in a ratio such that the mixture is heated to areducing temperature, contacting a mass of iron ore with the resultinggaseous mixture to reduce a portion of said ore; in a second reductiontreatment, mixing a stream comprising air maintained at a temperature ofbetween about 1400 F. and about 1600 F., and a stream comprising areducing gas said reducing gas being an effluent of and conveyed from athird reduction treatment conducted simultaneously with said secondreduction treatmen-t and maintained at an elevated temperature forcombustion with oxygen in said air, the mol ratio ot" oxygen to reducinggas being greater than that employed in said rst reduction treatmentsuch that the resultant gaseous mixture is heated to an elevatedreducing temperature, contacting a mass of said partially reduced ironore from said rst reduction treatment with theA resulting gaseousmixture to further reduce a portion of said ore to sponge iron; and in athird reduction treatment contacting a mass of said partially reducediron ore from said second reduction treatment with a stream comprising areducing gas maintained at a temperature between about 60 F. and about100 F. to reduce a further portion of said partially reduced ore tosponge iron.

9.l A method for reducing iron ore to produce sponge iron whichcomprises: in a rst reduction treatment, mixing a stream comprising airmaintained at a temperature between about 1400 F. and about 1600 F., anda stream comprising a partially spent reducing gas said partially spentreducing gas being an eiiluent of and conveyed from a secondre'ductiontreatment conducted simultaneously with said first reduction treatmentand maintained at an elevated temperature between about 600 F. and about1600 F. for 'combustion-With oxygen in said air, in a mol ratio suchythat the mixture is heated to a reducing temperature, contacting a massof iron ore with the resulting gaseous mixture to reduce a portion ofsaid ore; in a second reduction treatment, mixing a stream comprisingair maintained at a. temperature of between about 1400 F. and about 1600F., and a stream comprisingV a reducing gas said reducing gas being aneiiluent of and conveyed from a third reduction treatment conductedsimultaneously with said second reduction treatment and maintained at anelevated temperature between about 1500 F. and about 1600 F. forcombustion with oxygen in said air, the mol ratio of oxygen to reducinggas being greater than that employed in said first 10. The method ofclaim 2 in which the metal oxide comprises copper.

References Cited in the le of this patent and about 100 F. to reduce afurther portion of said 10 2,740,706

partially reduced ore to sponge iron.

UNITED STATES PATENTS Brown Dec. 3, 1935 Brown Dec. 18, 1934 SchmalfeldtFeb. 8, 1938 Pauli et al. Apr. 3v, 1956 Celada Aug. 18, 1959

1. A METHOD FOR REDUCING METAL OXIDES WHICH COMPRISES: IN A FIRSTREDUCTION TREATMENT, MIXING A STREAM COMPRISING AN OXYGEN-CONTAINING GASMAINTAINED AT A TEMPERATURE BETWEEN ABOUT 60*F. AND ABOUT 1800*F. AND ASTREAM COMPRISING A PARTIALLY SPENT REDUCING GAS. SAID PARTIALLY SPENTREDUCING GAS BEING AN EFFLUENT OF AND CONVEYED FROM A SECOND REDUCTIONTREAMTENT CONDUCTED SIMULTANEOUSLY WITH SAID FIRST REDUCTION TREATMENTAND MAINTAINED AT AN ELEVAGED TEMPERATURE FOR COMBUSTION WITH OXYGEN INSAID OXYGEN-CONTAINING GAS, IN A MOL RATIO SUCH THAT THE MIXTURE ISHEATED TO A REDUCING TEMPERATURE, CONTACTING A MASS OF METAL OXIDE WITHTHE RESULTING GASEOUS MIXTURE TO REDUCE A PORTION OF SAID METAL OXIDE;IN A SECOND REDUCTION TREATMENT, MIXING A STREAM COMPRISING ANOXYGEN-CONTAINING STREAM MAINTAINED AT A TEMPERATURE OF ABOUT 60*F. ANDABOUT 1800*F. AND A STREAM COMPRISING A REDUCING GAS SAID REDUCING GASBEING AN EFFLUENT OF AND CONVEYED FROM A THIRD REDUCTION TREATMENTCONDUCTED SIMULTANEOUSLY WITH SAID SECOND REDUCTION TREATMENT ANDMAINTAINED AT AN ELEVATED TEMPERATURE FOR COMBUSTION WITH OXYGEN IN SAIDOXYGEN-CONTAINING GAS, THE MOL RATIO OF OXYGEN TO REDUCING GAS BEINGGREATER THAN THAT EMPLOYED IN SAID FIRST REDUCTION TREATMENT SUCH THATTHE RESULTANT GASEOUS MIXTURE IS HEATED TO AN ELEVATED REDUCINGTEMPERATURE, CONTACTING A MASS OF SAID PARTIALLY REDUCED METAL OXIDEFROM SAID FIRST REDUCTION TREATMENT WITH THE RESULTING GASEOUS MIXTURETO FURTHER REDUCE A PORTION OF SAID METAL OXIDE TO THE METALLIC STATE;AND IN A THIRD REDUCTION TREATMENT CONTACTING A MASS OF SAID PARTIALLYREDUCED METAL OXIDE FROM SAID SECOND REDUCTION TREATMENT WITH A STREAMCOMPRISING A REDUCING GAS TO REDUCE A FURTHER PORTION OF SAID PARTIALLYREDUCED METAL OXIDE TO THE METALLIC STATE.